The present invention is related to sensing devices and, more particularly, to systems and methods for sensing the presence, position, shape and/or orientation of an object.
When locating, manipulating and fabricating semiconductor substrates or wafers, it is frequently necessary for a machine to determine whether a wafer is present at a particular location, and if so, its characteristics. In the prior art, there are many ways to make such a determination. One method includes measuring the position of the wafer on an end effector before the wafer is placed on a susceptor or other destination. Another method includes measuring the presence or absence of a wafer after it has arrived at its destination. Some systems employ optical detection devices, others make use of fluid pressure differentials. In any event, the solutions present in the prior art are not satisfactory for wafer sensing, positioning or characterization.
One example of an optical sensing system is provided in U.S. Pat. No. 5,768,125 by Zinger et al (xe2x80x9cZingerxe2x80x9d). In Zinger, an apparatus for transferring a substantially circular article from a first position to a second position compensates for misalignment of the article on a support arm. During movement of the support arm, the periphery of the circular article is detected and a correction of the movement of the support arm is generated. Zinger""s preferred embodiment employs a light detector in order to determine the object""s position. The light detector is comprised of a linear array of optical sensors, each sensor comprising a light emitting diode (xe2x80x9cLEDxe2x80x9d) and a light detecting photodiode. Light emitted from each LED is blocked as the object moves between the LED and the photodiode. The sensor registers this light blockage and sends a signal to a calculating means. In turn, the calculating means receives this data, and determines the wafer""s position and velocity, and repositions the wafer through manipulation of the support arm, as necessary.
Optical detection as described by Zinger is typically used to detect the lateral position of a flat substrate or semiconductor wafer. The vertical position of a horizontally oriented wafer and the alignment of such a wafer with respect to a support surface is significantly more complicated to accurately detect through optical detection. Consequently, optical detection is not favored for vertical positioning of horizontally oriented wafers, or for other similar applications.
U.S. Pat. No. 6,086,064 by Biegelsen et al. (xe2x80x9cBiegelsenxe2x80x9d) discloses a different method for detecting a wafer""s position. In Biegelsen, an object detection apparatus uses a pressurized fluid source and an interruptible jet sensor to determine the presence or absence of a wafer. In the preferred embodiment, a fluid jet flows across a gap towards a sensing port. When an object is present in the gap, the fluid jet is interrupted and a pressure change is detected and registered.
U.S. Pat. No. 6,280,291 by Gromko et al. (xe2x80x9cGromkoxe2x80x9d) discloses a wafer holder with a wafer presence sensor that makes use of a hydrodynamic pressure differential technique. In the preferred embodiment, a wafer sensor comprises a wafer holder, a liquid distribution system and a pressure sensor. The wafer holder is provided with a liquid distribution system comprising a central supply conduit in communication with a series of fluid passages opening up at a wafer support surface of the wafer holder. The wafer holder is configured such that, when a wafer is placed in the wafer holder the wafer covers the fluid passages, thereby restricting the flow of liquid from the liquid distribution system through the fluid passages. The liquid distribution system is provided with a pressure sensor to sense the pressure of fluid in the supply conduits supplying fluid to the passages. When the wafer holder holds a wafer, the restricted flow through the fluid passages causes an increase in pressure within the central supply conduit. The increase in pressure beyond a predefined threshold is detected by the pressure sensor and indicates that a wafer is present.
U.S. patent application Ser. No. 09/875,277 by Kuznetsov et. al., entitled APPARATUS FOR PROCESSING A WAFER, discloses an apparatus that comprises a support structure which manipulates a wafer during processing and an optical measuring means that determines the lateral position of the wafer prior to and during processing. In the preferred embodiment, the support structure is provided with at least one fluid supply channel opening at a wafer support surface of the support structure. This support structure provides fluidic support of the wafer during processing.
There are a many disadvantages inherent in the various positioning and detection solutions present within the prior art. In optical systems for example, the accuracy of the optical measurements depends on how well the position of these optical components are known. Currently, these optical systems are positioned using complicated mechanical means, which are not always accurate. Moreover, typical in line wafer centering systems are rather complex and expensive, and require many sensors to be accurately positioned. In addition, optical detection is difficult and frequently inaccurate. Likewise, typical fluid detection systems also leave much to be desired. Specifically, typical fluid detection systems detect only the presence or absence of an object. However, there are many applications where the measurement of a correct positioning of an object or a correct alignment of an object with respect to supporting plane is desirable in order to prevent damage to or loss of objects.
Accordingly, it is an objective of the present invention to provide a device and method to detect the presence, position, orientation and/or alignment of an object with respect to a supporting plane. It is another objective of the present invention to provide a device and method to determine the mechanical integrity and flatness of an object in order to prevent processing of objects that could damage a processing tool.
In satisfaction of these objectives, embodiments of the present invention provide devices and methods for receiving and depositing a substrate on a substrate support structure and verifying the correct shape, position and/or orientation of the substrate.
According to a first aspect of the invention, a substrate support and sensing apparatus for use in semiconductor processing is provided with a first substrate support structure, including at least one fluid channel configured to supply fluid to an underside of a substrate supported over the first support structure. At least one sensor is configured to measure a property of gas flow beneath the supported substrate and provide a signal indicative of the value of said property. A controller monitors the signal generated by the sensor and produces an indication of whether the substrate is oriented level relative to the first support structure.
In one embodiment, the first support structure comprises a table with three support pins having gas injection channels therein. The substrate is transferred from the first support structure to a second support structure (a support ring) by raising the second support structure or lowering the first support structure. A pressure sensor in each channel measures pressure while the second support structure supports the substrate over the first support structure, the pressures being correlated to distances from each of the support pins to the substrate.
In another embodiment, the first support structure comprises a plurality of gas ports providing a supporting gas cushion beneath the substrate. A separate channel is provided to sense pressure in a gap between the first support structure and the substrate supported thereover, the pressure being correlated with how level the substrate is relative to the first support structure and/or the curvature of the substrate.
According to a second aspect of the invention, a method of supporting and sensing a substrate for use in semiconductor processing is provided. The method includes supporting a substrate over a first support structure, which includes at least one fluid channel in communication with a gap between the first support structure and an underside of the supported substrate. Fluid flows through the fluid channel. A property of the fluid beneath the supported substrate is measured. The measured property is used to determine one or more of an orientation of the substrate with respect to the first support structure and a shape of the substrate.
According to a third aspect of the invention, a system for sensing the condition of a substrate over a support structure is provided. The system includes a substrate holder having an upper surface extending beneath a substrate supported thereover, the upper surface including a recess configured to accommodate the substrate therein. At least one fluid injection channel breaches the upper surface to inject fluid into a gap between the substrate and upper surface. A fluid pressure sensor is configured to measure pressure beneath the substrate. A controller connects to the pressure sensor and is configured to read the pressure sensed by the pressure sensor. The controller is also configured to compare the sensed pressure to a plurality of empirically determined pressure ranges associated with a corresponding plurality of substrate conditions to thereby determine a condition of the substrate based upon the sensed pressure.
According to a fourth aspect of the invention, a substrate support and sensing apparatus is provided with a first support structure for receiving and supporting a substantially horizontally oriented flat substrate. The first support structure is provided with at least three gas channels, which are configured to inject gas at spaced apart positions against a lower surface of a substrate supported above the first support structure. Each of the gas channels is provided with a sensor configured to generate a sensor signal relating to a property of gas flow through the channel. The apparatus also includes a second support structure, that is vertically movable with respect to the first support structure and configured such that a substrate supported on one of the support structures can be transferred to the other of the support structures. A drive mechanism moves the first and second substrate support structures with respect to each other. The drive mechanism has an encoder to read a vertical position. A controller is connected to the sensors and the encoder. The controller is configured to read, for each of the sensors, the vertical position indicated by the encoder together with the sensor signal, when a predetermined condition is achieved after dropping off the substrate.
In the illustrated embodiments, the systems and methods allow for the determination of the presence or absence of a wafer, its flatness and/or its orientation, through the use of data gathered from fluid pressure sensors.
These and other features and advantages of this invention are described in or are apparent from the following detailed description of the preferred embodiments.